2 Answers
2

If you're not hung up on the Hoya brand name, you can get neutral density filters in 2.4, 2.7 and 3.0 log densities (8, 9 and 10 stops) in the large square formats for Lee and Cokin filter holders, which will also make them usable on your other lenses. (The links are to product list pages at B&H.)

I must check out the thread type and diameter, maybe there even are adapters so I could pluck a larger filter?
– Andrei RineaDec 24 '11 at 9:53

Most of these solar filters fit over the end of the lens. They usually have a bit of gap to allow set screws for a snug fit. Given that the filter diameter of the lens you are using is 95mm, I'm guessing that a 4.10 inch diameter solar filter should drop over the hood of it readily.
– smigolDec 24 '11 at 10:03